Flashcards in Session 9 Deck (33)
What is Pharmacokinetics?
What the body does to a drug
What are the 2 formulations of a drug?
If the drug is a solid, what does rate of action depend on?
What are the sites of administration?
Local (eg oral, rectal)
Systemic - Enteral (Sublingual) Parenteral (IV, inhalation)
What is the advantage of local administration of drugs?
There are high concentrations of the drug at the site
There are less systemic effects
What is Oral Bioavailability?
Proportion of dose given orally (or any other route except IV) that reaches the systemic circulation in an unchanged form
How can Bioavailability be expressed?
How can you calculate the Bioavailability of a drug?
Area under curve for oral /
Area under curve for injection
What is the Therapeutic ratio?
Maximum tolerated dose (L50) /
Minimum effective dose (ED50)
Is a low or high Therapeutic ratio desirable?
High because this means the desired curve is far from the side effects curve
What is the First Pass effect?
A substance absorbed through the Ileum will enter the venous blood and passes directly to the liver where it is extensively metabolised before reaching the rest of the body.
Which routes can avoid the First Pass effect?
What is Drug Distribution?
Theoretical volume into which a drug has distributed assuming that this occurs instantaneously
How can you calculate Drug Distribution?
Amount given /
Plasma concentration at time 0
What exerts the effects of a drug?
The level of free drug in the blood
What is the main plasma protein that drugs can bind to?
When are protein binding actions important?
Drugs highly bound to albumin
Drug have a small volume of distribution
Drug has low therapeutic index
What is an Object (Class I) drug?
It is the drug that is medically active. It is used at a concentration which is much lower than the number of albumin binding sites
What is a Precipitant (Class II) drug?
The drug that is used at higher concentrations (Than the available binding sites) to displace the Class I drug from albumin.
What is the precipitant drug for Warfarin?
What is First order Kinetics?
The metabolism of the drug is proportional to drug concentration. Half life can be defined.
What would you see on a graph for First order Kinetics?
A straight line when a log scale is on the Y axis Vs time.
What is Zero order Kinetics?
Rate of elimination is constant regardless of concentration.
What would you see on a graph for Zero order Kinetics?
Straight line when normal (not log) plasma concentration is plotted against time (X)
How many half lives does it take for drug to reach a steady state?
5 half lives for all drugs regardless of dose or frequency
What is needed for an immediate effect of a drug?
A loading dose
How can you determine the loading dose?
Volume of distribution
What is the difference between First order Kinetics and Zero order kinetics?
First order gives a predictable Therapeutic response from dose increases
Zero order kinetics give a therapeutic response that can suddenly escalate as elimination mechanism saturate
What are some examples of Cytochrome P450 enzyme inducers?
Cigarettes (effects Theophylline drug)
Rifampicin (effects OC pill)